| Citation |
Bashirullah, A., Pasquinelli, A.E., Kiger, A.A., Perrimon, N., Ruvkun, G., Thummel, C.S. (2003). Coordinate regulation of small temporal RNAs at the onset of Drosophila metamorphosis. Dev. Biol. 259(1): 1--8. |
| PubMed Abstract |
The lin-4 and let-7 small temporal RNAs play a central role in controlling the timing of Caenorhabditis elegans cell fate
decisions. let-7 has been conserved through evolution, and its expression correlates with adult development in bilateral animals,
including Drosophila [Nature 408 (2000), 86]. The best match for lin-4 in Drosophila, miR-125, is also expressed during pupal
and adult stages of Drosophila development [Curr. Biol. 12 (2002), 735]. Here, we ask whether the steroid hormone ecdysone
induces let-7 or miR-125 expression at the onset of metamorphosis, attempting to link a known temporal regulator in Drosophila
with the heterochronic pathway defined in C. elegans. We find that let-7 and miR-125 are coordinately expressed in late larvae
and prepupae, in synchrony with the high titer ecdysone pulses that initiate metamorphosis. Unexpectedly, however, their expression
is neither dependent on the EcR ecdysone receptor nor inducible by ecdysone in cultured larval organs. Although let-7 and
miR-125 can be induced by ecdysone in Kc tissue culture cells, their expression is significantly delayed relative to that
seen in the animal. let-7 and miR-125 are encoded adjacent to one another in the genome, and their induction correlates with
the transient appearance of an approximately 500-nt RNA transcribed from this region, providing a mechanism to explain their
precise coordinate regulation. We conclude that a common precursor RNA containing both let-7 and miR-125 is induced independently
of ecdysone in Drosophila, raising the possibility of a temporal signal that is distinct from the well-characterized ecdysone-EcR
pathway.
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